1. Field of the Invention
This invention relates to heavy duty pneumatic radial tires which are applicable to heavy duty vehicles such as large construction vehicles.
2. Related Art Statement
In general, a heavy duty pneumatic radial tire 10 shown in FIG. 11 is adopted for large construction vehicles such as dumps, loaders, scrapers, and the like. The tire includes a carcass layer 11 reinforced by radially extending steel cords, a belt layer 16 arranged radially outward of the carcass layer 11 comprising four or more belt plies (four belt plies 12,13,14,15 in FIG. 1), and a tread 17 arranged radially outward of the belt layer 16. Oblique directions of the steel cords of each ply adjacent to each other are opposite and intersect.
However, when such a tire 10 is subjected to a heavy load during running, separations occur at both widthwise ends of belt plies 12,13,14,15.
In heavy duty pneumatic radial tires of this kind, deformations of the tread 17 force the inclined angles of the steel cords to deform in opposite directions in a so-called "Pantograph displacement". Also shearing strains occur because of the deformation of the steel cords in the rubber embraced between adjacent belt plies 12,13,14,15. The shearing strains progressively increase as displaced portions are nearer to ends of the belt plies in their width directions and have a maximum value at both ends of the belt ply 13.
In order to decrease the separations, therefore, an attempt has been made to restrain the shearing strains by changing the intersection angles of the steel cords of the belt plies with an equatorial plane E of the tires within limits which maintain performance of the tires, narrowing widths of the belt plies in their width directions within limits which maintain performance of the tires and arranging cushion rubbers at both of adjacent belt plies.
Although fairly good results have been obtained with such tires, separations could not be sufficiently prevented.